Parallel Dipole Line Trap Viscometer and Pressure Gauge

ABSTRACT

Techniques for gas analysis using a parallel dipole line (PDL) trap viscometer are provided. In one aspect, a gas analysis system is provided which includes: a PDL trap including: a pair of diametric cylindrical magnets, and a diamagnetic rod levitating above the magnets; and a motion detector for capturing motion of the diamagnetic rod. The motion detector can include a digital video camera positioned facing a top of the PDL trap so as to permit capturing video images of the diamagnetic rod and the system can include a computer for receiving and analyzing video images from the video camera. Methods for measuring gas viscosity and pressure using the PDL trap system are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/826,934 filed on Aug. 14, 2015, the contents of which areincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to techniques for gas viscosity andpressure analysis, and more particularly, to gas viscosity and pressureanalysis using a parallel dipole line (PDL) trap viscometer.

BACKGROUND OF THE INVENTION

Viscosity and pressure are two important physical parameters of a gasthat often need to be measured. Viscosity is a measure of fluid (or gas)resistance to gradual deformation by shear or tensile stress. Itprovides information about thermal-physical property and can also beused to probe intermolecular potentials. See, for example, G. P.Matthews et al., “An effective isotropic pair potential energy functionfor carbon dioxide,” Chemical Physics Letters, vol. 155, issue 6, pgs.518-520 (March 1989). In industrial setting, viscosity measurement isalso of great importance. For example, the viscosity of hydrocarbongases is an important factor in the petroleum industry. See, forexample, T. C. Davenport. “Viscosity in the petroleum industry,” PhysicsEducation 3, 139 (May 1968). It affects the quantity that can berecovered from a reservoir. In the semiconductor industry, the viscositydata of highly reactive gases used in semiconductor processing areneeded to calibrate mass-flow controllers and to model processes such aschemical vapor deposition. See, for example, J. Wilhelm, et al., “Animproved Greenspan acoustic viscometer,” International Journal ofThermophysics, vol. 21, issue 5, pgs. 983-997 (September 2000); and K.A. Gillis, et al., “Theory of the Greenspan viscometer,” The Journal ofthe Acoustical Society of America 114, pgs. 166-173 (July 2003).

The most common viscometers are falling ball viscometers, capillary tubeviscometers, oscillating-piston viscometers, vibrational viscometers,and rotational viscometers—most of which measure liquid viscosity. Themeasurement of gas viscosity is more challenging since the density andthe viscosity of gases are much lower. Thus modification of theseviscometers is needed in order to measure the viscosity of a gas.

One well-known viscometer for measuring gas viscosity is a doubleHelmholtz acoustic resonator. See, for example, K. A. Gillis et al.,“Greenspan acoustic viscometer for gases,” Rev. Sci. Instr. 67, 1850(June 1996). The performance of this viscometer device, however, dependson the response function of the system (which is determined by thegeometry of the system and the gas properties) and the instrumentationsetup is rather complex. As a result, this device cannot be used tomeasure the viscosity of a wide range of gases.

Gas or vacuum pressure measurement is also routinely needed. Variouspressure gauges are already available however they need to be calibratedwith other gauge and has limited accuracy. Very accurate vacuum pressuregauge based on gas viscosity measurement can be obtained using aspinning rotor gauge. However, this instrument is complex and expensive.

Therefore, an improved and more cost effective gas analysis apparatusthat can be used to measure viscosity and pressure in a wide range ofgases would be desirable.

SUMMARY OF THE INVENTION

The present invention provides techniques for gas analysis using aparallel dipole line (PDL) trap viscometer. In one aspect of theinvention, a gas analysis system is provided. The gas analysis systemincludes: a PDL trap including: a pair of diametric cylindrical magnets,and a diamagnetic rod levitating above the pair of diametric cylindricalmagnets; and a motion detector for capturing motion of the diamagneticrod. The motion detector can include a digital video camera positionedfacing a top of the PDL trap so as to permit capturing video images ofthe diamagnetic rod and the system can include a computer for receivingand analyzing video images from the video camera.

In another aspect of the invention, a method for analyzing a gas isprovided. The method includes the steps of: providing a gas analysissystem having i) a PDL trap having a pair of diametric cylindricalmagnets, and a diamagnetic rod levitating above the pair of diametriccylindrical magnets; and ii) a motion detector for capturing motion ofthe diamagnetic rod, wherein the PDL trap is encased within anenclosure; introducing the gas to the enclosure; initiating oscillationof the diamagnetic rod over the pair of diametric cylindrical magnets;recording motion of the diamagnetic rod using the motion detector;determining a damping time constant τ from the recorded motion of thediamagnetic rod; and calculating a viscosity μ of the gas using thedamping time constant t wherein, for example, μ=k_(V)/τ, and whereink_(V) is a viscosity measurement calibration factor for the gas analysissystem and is independent of the gas being analyzed.

In yet another aspect of the invention, another method for analyzing agas is provided. The method includes the steps of: providing a gasanalysis system having i) a PDL trap having a pair of diametriccylindrical magnets, and a diamagnetic rod levitating above the pair ofdiametric cylindrical magnets; and ii) a motion detector for capturingmotion of the diamagnetic rod, wherein the PDL trap is encased within anenclosure; introducing the gas to the enclosure; initiating oscillationof the diamagnetic rod over the pair of diametric cylindrical magnets;recording motion of the diamagnetic rod using the motion detector;determining a damping time constant τ from the recorded motion of thediamagnetic rod; and calculating a pressure p of the gas using thedamping time constant t wherein, for example, p=k_(P)/τ, and whereink_(P) is a pressure measurement calibration factor for the gas analysissystem and is independent of the gas being analyzed.

A more complete understanding of the present invention, as well asfurther features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a parallel dipole line (PDL) trapviscometer system according to an embodiment of the present invention;

FIG. 2a is a diagram illustrating a top-down view of the PDL trapviscometer system according to an embodiment of the present invention;

FIG. 2b is a diagram illustrating video motion analysis being used toextract the motion of a diamagnetic rod of the PDL trap viscometersystem according to an embodiment of the present invention;

FIG. 2c is a diagram illustrating underdamped oscillation of thediamagnetic rod according to an embodiment of the present invention;

FIG. 3a is a diagram illustrating underdamped oscillation with rods ofdifferent diameters according to an embodiment of the present invention;

FIG. 3b is a diagram illustrating damping time constant versus roddiameter according to an embodiment of the present invention:

FIG. 4 is a diagram of one exemplary configuration of the present PDLtrap system according to an embodiment of the present invention;

FIG. 5 is a diagram of an exemplary methodology for analyzing a gasusing the present PDL trap system according to an embodiment of thepresent invention; and

FIG. 6 is a diagram of an exemplary apparatus for implementing one ormore of the methodologies presented herein according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Provided herein are techniques for measuring the viscosity of an ambientgas utilizing an oscillating graphite rod trapped in a parallel dipoleline system. By capturing the oscillation (e.g., using video), thedamping lifetime of the oscillation can be extracted and the viscosityof the gas can be calculated. The system can also be utilized to measurepressure in a vacuum chamber at low pressure p regime (e.g., p<10⁻⁴bar). Compared to other existing technology, this system is compact, lowcost, can be miniaturized, and can be used to measure wide range ofgases

The present system makes use of an oscillating graphite rod trapped in aparallel dipole line (PDL) trap system. For a general description of aPDL trap system see, for example, Gunawan et al., “A parallel dipoleline system,” Applied Physics Letters 106, 062407 (February 2015)(hereinafter “Gunawan”); and U.S. Pat. No. 8,895,355 issued to Cao etal., entitled “Magnetic Trap for Cylindrical Diamagnetic Materials,” thecontents of each of which are incorporated by reference as if fully setforth herein.

A general overview of the present PDL trap-based gas analysis system anduse thereof to measure viscosity and/or pressure of an ambient gas isprovided in FIG. 1. As shown in FIG. 1, the present PDL trap gasanalysis system includes a pair of diametric cylindrical magnets 102 aand 102 b in which a diamagnetic rod 104, such as a graphite rod, istrapped. The diametric magnet has magnetization along the diameter ofthe magnet as shown in FIG. 1. Namely, as described in Gunawan acylindrical rod immersed in the magnetic field of the diametric magnetswill have an induced magnetization. Since the rod is diamagnetic, theinduced magnetization is opposite to the magnetic field and tends tomove it towards a region with minimum field and produces levitation oftrapping effect. Thus, the diamagnetic rod levitates above the diametricmagnets. The length of the rod (l) is chosen to allow stable trappingcondition e.g., approximately 0.15 L<l<0.9 L where L is the length ofthe diametric magnet. Further, as described in Gunawan, this system alsoyields a one-dimensional camelback potential along the longitudinal (z)axis stemming from the magnetic field distribution. See FIG. 1. It hasbeen found herein that this weak confinement allows a graphite rod (inone exemplary embodiment a mechanical pencil lead) trapped in thissystem to oscillate. See the double sided arrow in FIG. 1 whichindicates the path of oscillation of the diamagnetic rod over themagnets 102 a and 102 b. An actuator (described below) can be used totilt the trap to initialize the oscillation of the diamagnetic rod. Seethe double sided arrow in FIG. 1 which indicates that the trap can bebriefly tilted to initiate the oscillations.

This oscillation can be recorded with a motion detection system.According to an exemplary embodiment, the motion detection systemincludes a video camera 106 that is positioned facing a top of the PDLtrap so as to permit capturing video images of the diamagnetic rod. Themotion data can be sent to a computer 108. The computer will analyze thedata, extract the damping time constant (due to the presence of anambient gas), and calculate the viscosity and/or pressure of the ambientgas. An exemplary apparatus that may be implemented as computer 108 isprovided in FIG. 6, described below.

One of the advantages of the present PDL trap gas analysis system is itslow-cost production and maintenance. It is also compact and requires arelatively small amount of gas for measurement. This is particularlyimportant when the gas is rare or expensive. Furthermore, this systemcan be miniaturized which might be valuable for certain industryapplications.

The magnetic field distribution of the present PDL trap can be describedas the field due to magnetic parallel dipole line. The trap has a weakcamelback confinement potential (see, for example, FIG. 1) along thez-axis that allows the diamagnetic rod to oscillate. A top-down view ofthe PDL trap is shown in FIG. 2a . As shown in FIG. 2a , the diamagneticrod (in this case a graphite rod) will oscillate to the left and to theright along the z-axis. As highlighted above, these oscillations can becaptured using video motion analysis. See FIG. 2b . According to anexemplary embodiment, a digital video camera is used for the videomotion analysis. The pixels in a digital camera collect photons whichare converted into an electrical charge that represents intensity.During the motion analysis, the intensity of the image pixels can bemeasured from each video frame. See FIG. 2b wherein the pixel intensityis plotted along the z-axis. The position of the rod can be determinedby choosing a certain intensity value that marks the edge of the rodcalled “edge threshold.” The plot in FIG. 2b shows the positioning ofthe graphite rod as it appears in FIG. 2a . By capturing video of thetrapped rod, one can obtain the (damped) oscillation curve of the rodand extract its parameters such as the oscillation period (T) and thedamping time constant (τ). See FIG. 2c , wherein t is time, l is thelength of the rod, and z_(R) is the rod position or displacement.

The oscillation damping of the rod is due to the viscous drag (friction)of the (ambient) gas surrounding the rod. In a simple approximation of ashort cylindrical rod with diameter comparable to its length, the gasviscosity μ can be calculated from the damping time constant (τ) as:

$\begin{matrix}{\mu \sim \frac{2{\rho\pi}\; {rl}}{C_{D}\tau}} & (1)\end{matrix}$

wherein ρ, r, and l are the mass density, radius, and length of the rodrespectively, and CD is the drag coefficient that depends on thegeometry of the rod such as the length (l) and radius (r). For examplewhen l/r>4. C is approximately 0.81 (see, for example, Fluid DynamicDrag. Hoerner, Hoerner Fluid Dynamics, Chapter 3, pg. 12 (3-12), 1965).For a fixed setup (e.g., the present PDL trap with a rod of known/fixeddimensions), these various factors can be lumped together as a viscositycalibration factor k_(V):

μ=k _(V)/τ  (2)

The factor k_(V) is an experimental or calibration constant independentof gas. It can be measured using gas of a known viscosity, and this stepbecomes the calibration step. For instance, the present PDL trap with arod of known dimensions can be used along with an ambient gas of knownviscosity. The oscillations of the rod can be measured using (e.g.,video) motion analysis, and the damping time constant τ can bederived—as described above. Since both the gas viscosity μ and thedamping time constant τ are known, then the factor k_(V) in Equation 2can be calculated.

The present system can also be utilized as a pressure gauge, i.e., asystem to measure pressure at a low pressure p regime (p<10⁻⁴ bar),e.g., for a vacuum chamber. At a high pressure regime, where the gasmean free path is much shorter than the feature size of the system,e.g., p>10⁻⁴ bar, the gas viscosity is independent of pressure. Howeverthe “viscosity” drops at low pressure regimes and it's approximatelyproportional to the gas pressure. Strictly speaking at this low pressureregime, the “viscosity” being measured is no longer a characteristic ofthe gas—but rather is due to the geometrical characteristics of thevacuum chamber. This is because the gas mean free path is much longerthan the feature size of the measurement system, e.g., the PDL trap. Asystem based on friction drag of a magnetically levitated rotating ball(called spinning rotor gauge) has been demonstrated to measure pressure.This system is accurate and serves as an absolute pressure measurementtool that can be used to calibrate other types of pressure gauges. See,for example. Boffito et al., “Spinning rotor gauge in the range from10⁻⁴ Pa to atmosphere,” J. Vac. Sci. Technol. A 15(4), pgs. 2391-2394,July/August 1997, the contents of which are incorporated by reference asif fully set forth herein. A similar principle can be used to performpressure measurement using the present PDL trap system. In this systemthe rate of changes of rotor angular velocity is proportional to thepressure p and the mean velocity of the gas v_(g) at pressure pimpinging on the rotor surface. i.e., (dω/dt)/ω˜−pv_(g).

The present PDL trap system can be used for pressure measurement at lowpressure regime (e.g., p<10⁻⁴ bar) by the same measurement of the rodoscillation damping time constant τ. The damping time constant τ isrelated to the pressure as: τ˜1/pv_(g). Since v_(g) depends on pressure,the pressure can be simplified as a function of damping time constant τas:

p=k _(P)/τ  (3)

where k_(P) is an experimental constant or pressure calibration factorfor the system. It can be measured using a known gas pressure p (e.g.,the pressure of a gas measured using another separate pressure gauge),and this step becomes the calibration step. For instance, the presentPDL trap with a rod of known dimensions can be used along with anambient gas at a known pressure. The oscillations of the rod can bemeasured using (e.g., video) motion analysis, and the damping timeconstant τ can be derived—as described above. Since both the pressure pand the damping time constant τ are known, then the factor k_(P) inEquation 3 can be calculated. It is notable that the pressure versus tcan also be characterized across a wide range of pressures to anticipatenon-linear behavior, e.g., at a high pressure regime (p>10⁻⁴ bar) wherethe damping time constant tends to be constant due to constant gasviscosity versus pressure (i.e., near a high pressure regime (e.g.,p>10⁻⁴ bar) the damping time constant could start to be non-linear withrespect to pressure and ultimately becomes constant at higher pressuredue to constant viscosity—however pressure measurements can still beperformed, except that the damping time constant vs. pressure needs tobe calibrated/plotted in this non-linear regime). Further, it is notablethat the damping time constant τ actually also depends on the diameter dof the levitated rod. See, for example, FIGS. 3a-b . Specifically, FIG.3a is a diagram illustrating underdamped oscillation (i.e., where theamplitude gradually decays to zero) of rods of diameter d of 0.3millimeters (mm) and 0.9 mm. As shown in FIG. 3a , the damping timeconstant τ (measured in seconds (s)) is greater (damping is weaker) withthe larger diameter rod. Similarly. FIG. 3b which plots rod diameter d(measured in mm) as a function of the damping time constant τ (measuredin s) shows that τ increases (damping becomes weaker) with a larger roddiameter. This aspect is useful for tuning the dynamic range of themeasurements based on the sensitivity of the system. For instance, whenthe viscosity of the gas being measured is large, a rod having a largerdiameter can be used to increase the sensitivity of the measurement orto ensure that the measurement can be performed in a reasonably shortamount of time.

Namely, the greater the viscosity of the gas, the more friction the gaswill impart on the oscillating rod. Thus, by increasing the diameter ofthe rod, the effect of the damping (due to the gas) can bedecreased/weakened in order to permit the above-described viscositymeasurements to be made. To look at it another way, if a (relatively)small diameter rod was use to measure the viscosity of a (relatively)higher viscosity gas, then the damping effect (of the gas) might notpermit the transient oscillation of the rod needed to extract theviscosity. To give a simple example to illustrate this point, silane(SiH₄) and ammonia (NH₄) are common chemical vapor deposition (CVD) andatomic layer deposition (ALD) precursors. Silane has a greater viscosity(e.g., 1.070×10⁻⁴ poise) than ammonia (e.g., 9.193×10⁻⁵ poise). Thus, ina system employing silane as the ambient gas one might choose to use arod of a greater diameter (e.g., d=0.9 mm) than when ammonia is theambient gas (e.g., d=0.3 mm).

Another consideration, however, is the length of time needed to make themeasurement. For instance, referring to FIG. 2c , the oscillation periodT and the damping time constant τ are extracted from the rod oscillationcurve that occurs over a time t. Depending on the diameter of the rod,the time t over which transient oscillation of the rod occurs varies.Compare, for example, the examples shown in FIG. 3a with rods ofdiameter d=0.3 mm and d=0.9 mm which exhibit transient oscillation overa period of about 15 seconds (s) and about 27 s, respectively. Thus, fora gas of a given viscosity, the rod diameter can be varied to adjust themeasurement time. According to an exemplary embodiment, the rod used inthe present system has a diameter of from about 0.3 mm to about 1.3 mm,and ranges therebetween.

FIG. 4 is a diagram of one exemplary configuration of the present PDLtrap system. In the example shown in FIG. 4, the PDL trap system isencased within an enclosure. This will enable an ambient gas to becaptured for measurement. Namely, the enclosure is fitted with an inletdoor, through which the gas can be introduced into the enclosure (seegas inlet and inlet door). The present PDL trap (see PDLtrap/diamagnetic magnet pair and graphite rod) is located within theenclosure situated on a tiltable platform.

The tiltable platform permits, via an actuator (in this case a shapememory alloy), one end of the PDL trap to be momentarily lifted and thenreturned to a horizontal orientation which serves to initialize theoscillation of the graphite rod levitating above the magnets. Namely, asshown in FIG. 4, the tiltable platform is attached to an inner surfaceof the enclosure via a pivoting link. The actuator is attached both tothe top of the enclosure and to an end of the platform opposite thepivoting link. According to an exemplary embodiment, the actuator is ashape memory alloy that is configured to contract by a constant amountwhen a current is applied to it—pulling the end of the tiltable platformtoward the top of the enclosure, thereby raising the end of the tiltableplatform by that (constant) amount. When the current is removed, theactuator returns to its relaxed state, and the tiltable platform (andPDL trap) are returned to a horizontal orientation. Shape memory alloywires which may be used as an actuator are commercially available, forexample, from Dynalloy. Inc., Irvine, Calif. The use of a tiltableplatform and shape memory alloy actuator are merely an example meant toillustrate the present techniques. In practice, any means for joltingthe platform/PDL trap to initiate oscillation of the rod may be employedsuch as using a solenoid actuator, a small electric motor, etc.According to an exemplary embodiment, the platform/PDL trap starts at ahorizontal orientation (i.e., at an angle θ of 0 degrees (°) relative tothe bottom of the enclosure—see FIG. 4). When the actuator is activated,the platform/PDL trap is raised at an angle θ of from about 10° to about30°, and ranges therebetween relative to the bottom of the enclosure,for a duration of from about 1 second to about 3 seconds, and rangestherebetween, after which the platform/PDL trap is returned to thehorizontal orientation.

Stopper guards are located on opposite ends of the PDL trap (i.e., onopposite ends of the path of oscillation of the rod along thez-axis—see. e.g., FIG. 2a ). The stopper guards serve to physicallyprevent the levitating graphite rod from travelling past the ends of themagnets during oscillation. The stopper guards may be made from anysuitable non-metallic/non-magnetic material, such as plastic, rubber,etc.

In this exemplary embodiment, the oscillating motion of the rod iscaptured using a digital video camera. As shown in FIG. 4, the digitalvideo camera is located in a top of the enclosure and is positionedfacing the top of the PDL trap and the rod (i.e., the video camera has atop down view of the PDL trap and oscillating rod—in the same manner asshown in FIG. 2a ). As described above, the video camera will capturevideo images of the rod oscillating over the magnets.

As shown in FIG. 4, the video camera, the actuator, and the enclosureinlet door are all controlled by a microcomputer. An exemplary apparatusthat may be implemented as the microcomputer is provided in FIG. 6,described below. Specifically, the microcomputer will coordinateopening/closing the inlet door to capture a gas sample within theenclosure, activate the actuator (e.g., provide momentary current toshape memory alloy) to tilt the platform and thereby initiateoscillation of the rod, and start the video camera to record theoscillations. In turn, the video camera will relay the digital videoimages of the oscillating rod to the microcomputer where the data isanalyzed (as described in detail above) to extract the oscillation andits parameters (such as the oscillation period T and the damping timeconstant r) which are used to calculate the viscosity and/or pressure ofthe gas. The results of the analysis can be revealed on a display orreadout, such as a standard computer monitor.

An exemplary methodology 500 for analyzing a gas using the present PDLtrap system is now described by way of reference to FIG. 5. The processbegins in step 502 by capturing a sample of the gas. According to anexemplary embodiment, the PDL trap system is configured as shown in FIG.4 to include an inlet door through which the gas is introduced to theenclosure. As provided above, the inlet door can be controlled by amicrocomputer which can open the inlet door (e.g., via a standard motorgear drive or other similar actuator) to receive the gas sample, andthen close the inlet door to ensure that no air agitation occurs duringthe viscosity measurement. By way of example only, the microcomputer maycontrol opening the inlet for a certain duration (e.g., from about 1second to about 10 seconds, and ranges therebetween), during which timean ambient gas passively enters the enclosure. Alternatively, a gassample might be injected into the enclosure through the inlet opening.

In step 504, oscillation of the rod over the magnets is initiated. Asprovided above, oscillation of the rod can be initiated simply byjolting the PDL trap. According to an exemplary embodiment, the PDL trapsystem is configured as shown in FIG. 4 to include an actuator (such asa shape memory alloy, solenoid actuator, or electric motor attached tothe platform and to the top of the enclosure) that is configured to tiltthe PDL trap thereby initiating oscillation of the rod. For instance,using a shape memory alloy actuator as an example, a current can beapplied to the shape memory alloy to cause it to constrict (by aconstant amount)—pulling the end of the tiltable platform toward the topof the enclosure, thereby raising the end of the tiltable platform. Asolenoid actuator or electric motor would operate in the same manner totilt the platform. For instance, with a linear solenoid actuator anapplied current moves a plunger a fixed distance. When the current isremoved, the plunger returns to its original position. This movement ofthe plunger can be used to tilt the platform. Similarly, an electricmotor with a drive gear can be used to raise/lower the platform when acurrent is supplied to the motor. Preferably, stopper guards areimplemented (as described above) in order to prevent the rod fromtravelling past the ends of the magnets.

In step 506, once jolted, one must wait (approximately five oscillationperiods) for transient oscillation of the rod to occur. During thisinitial transient period, the rod could develop some additional randommotion or oscillation mode (e.g., torsional mode along its verticalaxis) that decays more quickly.

In step 508, video of the rod oscillation is recorded. According to anexemplary embodiment, the PDL trap system is configured as shown in FIG.4 including a digital video camera and a microcomputer that coordinatesthe video camera with the inlet door and the actuator. Namely, followingactivation of the actuator to initiate motion of the rod, themicrocomputer then begins the video camera recording the oscillatingmotion of the rod. The video is then relayed from the video camera tothe microcomputer where it is analyzed—see step 510.

In step 510, the video is analyzed. Video motion analysis can be carriedout, as described above, to extract the oscillation of the rod and itsparameters, such as the oscillation period T and the damping timeconstant t. According to an exemplary embodiment, the PDL trap system isconfigured as shown in FIG. 4 and the video motion analysis is carriedout by the microcomputer.

As provided above, an initial calibration of the system may beperformed, i.e., prior to measuring the viscosity of an unknown gas. Tocalibrate the system, steps 502-510 can be carried out with a rod ofknown/fixed dimensions, and a gas of known viscosity and/or pressure.Based on the calibration via steps 502-510, the damping time constant τcan be measured and, along with the known gas viscosity, used todetermine the factor k_(V) (see Equation 2)—which as described above isan experimental viscosity constant independent of the gas beingmeasured. Similarly, the damping time constant τ (measured in steps502-510) along with a gas at a known pressure (i.e., measured separatelywith another pressure gauge) can be used to determine the factor k_(P)(see Equation 3)—which as described above is an experimental pressureconstant independent of the gas being measured.

If the process is in this calibration phase (Yes), then as per step 512methodology 500 ends (since the viscosity of the gas for calibrationpurposes is already known), and the process can be repeated with anunknown gas sample. In subsequent iterations, the same/fixed roddimensions for which the system has been calibrated are used.Alternatively, if it is determined in step 512 that this is not thecalibration phase of the process (No) (e.g., the system has already beencalibrated in an earlier run, and is now being used to measure anunknown sample), then the process continues at step 514 to calculate the(unknown) viscosity and/or pressure of the gas.

Namely, in step 514 at high pressure regimes (e.g., p>10⁻⁴ bar) the(unknown) viscosity of the gas can be calculated using Equations 1 and 2above, and at low pressure regimes (e.g., p<10⁻⁴ bar) the (unknown)pressure of the gas can be calculated using Equation 3 above. It may bedesirable to take multiple readings to increase the accuracy of themeasurement. That decision is made in step 516, i.e., whether or not torepeat the measurement process. If it is determined in step 516 (Yes) toperform multiple readings, then the process can be repeated beginning atstep 504 where the PDL trap is jolted (as described above) to initiateoscillation of the rod and, once transient oscillation is achieve,another reading is performed using video motion analysis, etc. Whenmultiple readings are made, the average of the readings can be taken asthe measured gas viscosity. By way of example only, the average of from3-10 iterations of the process may be employed. If/when it is determinedin step 516 (No) that no more iterations are needed, then the processends.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Turning now to FIG. 6, a block diagram is shown of an apparatus 600 forimplementing one or more of the methodologies presented herein. By wayof example only, apparatus 600 can be implemented as the computer108/microcomputer in FIG. 1 and FIG. 4, respectively.

Apparatus 600 includes a computer system 610 and removable media 650.Computer system 610 includes a processor device 620, a network interface625, a memory 630, a media interface 635 and an optional display 640.Network interface 625 allows computer system 610 to connect to anetwork, while media interface 635 allows computer system 610 tointeract with media, such as a hard drive or removable media 650.

Processor device 620 can be configured to implement the methods, steps,and functions disclosed herein. The memory 630 could be distributed orlocal and the processor device 620 could be distributed or singular. Thememory 630 could be implemented as an electrical, magnetic or opticalmemory, or any combination of these or other types of storage devices.Moreover, the term “memory” should be construed broadly enough toencompass any information able to be read from, or written to, anaddress in the addressable space accessed by processor device 620. Withthis definition, information on a network, accessible through networkinterface 625, is still within memory 630 because the processor device620 can retrieve the information from the network. It should be notedthat each distributed processor that makes up processor device 620generally contains its own addressable memory space. It should also benoted that some or all of computer system 610 can be incorporated intoan application-specific or general-use integrated circuit.

Optional display 640 is any type of display suitable for interactingwith a human user of apparatus 600. Generally, display 640 is a computermonitor or other similar display.

Although illustrative embodiments of the present invention have beendescribed herein, it is to be understood that the invention is notlimited to those precise embodiments, and that various other changes andmodifications may be made by one skilled in the art without departingfrom the scope of the invention.

What is claimed is:
 1. A gas analysis system, comprising: a paralleldipole line (PDL) trap comprising: a pair of diametric cylindricalmagnets, and a diamagnetic rod levitating above the pair of diametriccylindrical magnets; and a motion detector for capturing motion of thediamagnetic rod.
 2. The gas analysis system of claim 1, wherein thediamagnetic rod comprises a graphite rod.
 3. The gas analysis system ofclaim 1, wherein the diamagnetic rod has a diameter of from about 0.3 mmto about 1.3 mm and ranges therebetween.
 4. The gas analysis system ofclaim 1, wherein the PDL trap is encased within an enclosure.
 5. The gasanalysis system of claim 4, wherein the enclosure comprises an inletdoor to permit a gas to be introduced into the enclosure.
 6. The gasanalysis system of claim 5, further comprising: a platform, on which thePDL trap is situated, attached to an inner surface of the enclosure viaa pivoting link.
 7. The gas analysis system of claim 6, furthercomprising: an actuator attached to a top of the enclosure and to an endof the platform opposite the pivoting link.
 8. The gas analysis systemof claim 7, wherein the actuator comprises a shape memory alloy.
 9. Thegas analysis system of claim 8, wherein the shape memory alloy isconfigured to contract by a constant amount with an applied current. 10.The gas analysis system of claim 7, wherein the actuator comprises asolenoid actuator.
 11. The gas analysis system of claim 7, wherein theactuator is configured to raise the platform to an angle θ of from about10° to about 30° and ranges therebetween relative to a bottom of theenclosure.
 12. The gas analysis system of claim 1, further comprising:stopper guards on opposite ends of the PDL trap to prevent thediamagnetic rod from traveling past the ends of the PDL trap.
 13. Thegas analysis system of claim 12, wherein the stopper guards are formedfrom a non-magnetic material.
 14. The gas analysis system of claim 13,wherein non-magnetic material is selected from the group consisting of:rubber and plastic.
 15. The gas analysis system of claim 1, wherein themotion detector comprises a digital video camera positioned facing a topof the PDL trap so as to permit capturing video images of thediamagnetic rod.
 16. The gas analysis system of claim 15, furthercomprising a computer for receiving and analyzing video images from thedigital video camera.
 17. A gas analysis system, comprising: a PDL trapencased within an enclosure, the PDL trap comprising: a pair ofdiametric cylindrical magnets, and a diamagnetic rod levitating abovethe pair of diametric cylindrical magnets; and a motion detector forcapturing motion of the diamagnetic rod, wherein the motion detectorcomprises a digital video camera at a top of the enclosure positionedfacing a top of the PDL trap so as to permit capturing video images ofthe diamagnetic rod.
 18. The gas analysis system of claim 17, furthercomprising: a platform, on which the PDL trap is situated, attached toan inner surface of the enclosure via a pivoting link.
 19. The gasanalysis system of claim 18, further comprising: an actuator attached toa top of the enclosure and to an end of the platform opposite thepivoting link.
 20. The gas analysis system of claim 19, wherein theactuator comprises a shape memory alloy.